N/A
The present invention relates generally to telephone instruments, and more specifically to telephone instruments that are directly connected to a data LAN (Local Area Network).
As it is generally known, telephone systems for business use normally consist of a central switch or Private Branch exchange (PBX), illustrated by PBX 16 shown in FIG. 2, which connects to telephones throughout the business via a twisted pair wire 14 and 15. An example of such a system configuration is depicted in FIG. 2. In most cases the PBX 16 will use a single twisted pair cable 14 to connect with the telephone instrument 13. During operation of the system shown in FIG. 2, the PBX 16 sends signals to and receives signals from the telephone instruments 10 and 13 via a frequency translated modem system.
Existing PBX systems typically use dedicated wiring, shown as multi-pair cables 15 in FIG. 2, connected to the PBX 16. The multi-pair cables 15 are connected to punch-down blocks 12. The punch-down blocks 12 are normally placed in a closet on the floor of the office building, near the telephone instruments 10 and 13. The individual station cables 14 are also connected to the punch-down blocks 12. The station cables 14 lead to the wall jacks 11. The telephone instruments 10 and 13 are connected to the system via instrument cables 18 to the wall jack 11. The telephones 10 and 13 are powered via a DC current that is carried by the same pair as that used for signaling. Telephone calls are made outside the premises via a Wide Area Network (WAN) link 17 connected to the PBX unit 16. The WAN link 17 is often a multi-channel circuit, such as what are commonly referred to as xe2x80x9cT1xe2x80x9d or xe2x80x9cPRIxe2x80x9d links.
The typical existing PBX system requires dedicated wiring. It does not share wiring with the data LAN that is common in most businesses. Thus, two wiring networks are normally required within an office building, one for data and one for telephones.
Recently, a technique for creating a xe2x80x9cvirtualxe2x80x9d PBX has been employed that is referred to as a xe2x80x9cLAN-PBX.xe2x80x9d In this technique, the telephone instrument uses a common Ethernet LAN cable, instead of a single twisted pair cable, to communicate with the PBX. An illustrative LAN-PBX system is shown in FIG. 3. In this case, the PBX is actually a telephony server 27 with switch control software that is connected to the LAN. The telephones 21, 23 and 25 are Ethernet LAN devices that also communicate over the LAN. Thus the telephony application, consisting of telephones 21, 23, and 25, and a telephony server 27, attached to a WAN interface 28, can utilize the same switch 22 as the computers 24 and network data servers 26. The advantage of the LAN-PBX architecture shown in FIG. 3 is that the telephones 21, 23 and 25 can use the same wiring and data switches as are used to convey LAN data, thus resulting in increased flexibility and overall lower cost.
A significant problem with the LAN-PBX approach illustrated in FIG. 3 is that telephony data has different delivery requirements than normal computer and server data. Telephony data must be delivered on-time (within a few milliseconds), and without delay, on a continuous basis. Normal computer data can usually suffer delays of a few hundred milliseconds without difficulty. Delays of this magnitude (a few hundred milliseconds) are common in computer networks. They occur because computer data is transmitted at a variable and unpredictable rate. As a result, there can be momentary blockages and congestion, even though the network has adequate bandwidth for the average data load.
Existing LAN-PBX systems attempt to solve this problem by giving telephony data priority over computer data. In the event of data congestion, such existing systems pass telephony data ahead of computer data. This priority system can work when only one telephone with data to transmit is present on a given circuit at a given time. However, when a circuit must carry multiple telephone connections, the congestion problem can arise again. This happens because multiple packets with equivalent priority give no means for arbitration. Consider the Telephony Server Link 30 shown in FIG. 3. When multiple telephone calls are placed to the WAN interface 28 they must all pass through the link 30. In that event, multiple telephony data packets, all having equivalent priority, may simultaneously require shared telephony server link 30 resource. A priority mechanism cannot distinguish between them, and the packets cannot interfere with one another.
Another problem with the LAN-PBX is that Ethernet cables and switches make no provision for providing power. Generally, in an Ethernet-based system as shown in FIG. 3, power is provided by a separate telephone power supply 29 at each station or instrument. As a result, it is difficult to operate the entire network in the event of a power outage. The user must provide backup power at each instrument, instead of centrally, as is possible with a typical PBX system.
Additionally, both PBX and LAN-PBX systems have difficulty supporting multiple types of instruments, in a flexible manner. Some instruments need many features, while others need only basic capabilities. There is no convenient way to extend or modify an instrument""s behavior without complete replacement. That is, accessories to instruments are rarely supported.
Typical existing PBX systems, such as the one illustrated in FIG. 2, suffer from another problem. The telephone number of a particular handset is determined by the circuit jack to which it is attached. This is inconvenient, as users may need to move a handset from one jack to another, while maintaining the same telephone number. Under such circumstances, the typical PBX user must reconfigure the switch.
Finally, existing LAN telephones are operated by internally stored control software. Such software must normally be installed separately into each instrument. This procedure makes software updates and corrections difficult, since each instrument must be reloaded individually.
For the reasons stated above, it would be desirable to have a LAN telephone instrument system which uses the same wiring system as is used to convey data transmission, and which operates without the delays that may occur in existing systems. It would further be desirable to have a LAN telephone instrument system which a) operates using power supplied over Ethernet cables, b) provides for accessory attachments, c) can maintain a phone number even when moved to a new jack, and d) enables convenient downloading of software.
Consistent with the present invention, a LAN telephone instrument is disclosed. The disclosed LAN telephone uses a Time-based Routing (TBR) technique to schedule packets of voice-telephony data. Through use of the Time-Based Routing technique, the problems of multiple LAN telephone instruments sending contending or colliding packets is avoided. The disclosed LAN telephone operates in connection with a system for providing power to the LAN telephone instrument through an attached LAN cable. This allows multiple LAN telephone instruments to be centrally powered.
The disclosed LAN telephone further includes a technique for automatically providing a remote switch with location of the LAN telephone instrument, thus enabling automatic direction of calls thereto. Additionally, a system for remote configuration of the control program of a LAN telephone instrument is also disclosed, which employs the LAN itself to provide the data connection over which the control program is downloaded.
The present disclosure further includes a system for attachment of telephone instrument accessories, which may be used to extend the functional capability of the LAN telephone instrument. An illustrative accessory, an operator console, is described in detail.